A conventional design for a head and disk assembly of a fixed disk drive calls for a bowl-shaped base casting with integral floor wall and four sidewalls extending upwardly at the periphery thereof, and a separate, flat top cover for enclosing an interior space defined by the base casting. One or more data storage disks are typically mounted in the interior space upon a spindle assembly most commonly including an internal brushless DC spindle motor. Data transducer heads for writing data onto data storage surfaces of the disks, and for reading back data from the disks are gang-mounted to a mass balanced rotary voice coil actuator assembly. Driving currents applied to an actuator coil cause the actuator assembly to rotate and thereby position the heads at "cylinder locations" which comprise concentric data storage track locations at each data storage surface.
It has been conventional design practice to attach a center shaft of the spindle motor and a center shaft of the rotary actuator to both the floor wall of the base casting and to the top cover. Dual attachments of these shafts or structures at the top and bottom rigidized the resultant structures and thereby improved their mechanical performance characteristics. Unfortunately, this desirable mechanical arrangement resulted in amplification of acoustic noise generated by the spindle motor and rotary actuator.
Acoustic noise generated in disk drive spindles may be attributable to spindle rotational speed. It may also be attributable to step function driving signals applied to operate a direct drive, brushless DC spindle motor. At the switching points of the step function driving signals, the torque produced in adjacent phase windings is equal, so there is no discontinuity in total torque produced by the spindle motor. However, the point of application of the torque force moves in location from phase winding to phase winding in the motor stator. At each commutation point, one phase sees a positive step of force and another sees a negative step of force. These abrupt forcing functions at the commutation point cause mechanical deformation and result in acoustic noise. Similar noise-producing phenomena occurs within the voice coil rotary actuator structure.
Contemporary disk drives are being designed with higher spindle speeds and faster access times. Both of these improvements, while enhancing storage capacities and reducing data access times, have resulted in increased acoustic noise.
It is well understood that one of the main noise emitters in a head and disk assembly is the "drum-like" top cover and bottom wall which are both excited by the spindle motor and the rotary actuator. Acoustic noise measurements have shown that most acoustic noise products generated in fixed disk drives emanate from the top cover and bottom wall. A very small component of the overall noise level emanates in directions leading away from the sidewalls.
One prior attempt to reduce acoustic noise within a head and disk assembly called for decoupling the spindle and actuator mechanism from its enclosure by employing a plurality of rubber isolator mounts. While that approach reduced unwanted acoustic noise, the rubber isolator mounts created a low frequency mode of the head and disk assembly, resulting in degraded vibration performance.
The creation of a separate outer package for a disk drive in order to isolate an inner drive assembly presents serious issues related to the desired to maintain existing disk drive length, width and height dimensions, collectively known as "form factor". The need has been particularly acute to maintain a low height profile or dimension.
Thus, a hitherto unsolved need has existed for a fixed disk drive having reduced acoustic noise without degraded performance characteristics and without enlarging the form factor of the drive.